Known in the art are aircraft air-cushion landing gears (cf. the air-cushion landing gear for the amphibious aircraft "La-4" of the "Bell Aerosystems" company (USA), and U.S. Pat. No. 3,275,270) comprising one or two units in the form of elastic inflatable cells secured to the underside of the fueslage in the symmetry plane of the aircraft.
If the landing gear is composed of a single unit, its only cell is located near the centre of gravity. In a two-unit version, one of the cells is arranged in the same manner as in the one-unit version with the second unit being located in front of the first one.
Each inflatable cell is, in plan view, on a generally annular configuration extended longitudinally and, when inflated, serves as a flexible curtain confining open spaces therewithin under the aircraft fuselage, supplied thereto is compressed air by means of injecting or compressor devices to create an air cushion under the aircraft for sustaining the latter in air in close proximity to the runway surface of an airfield during take-off, running and taxiing.
Compressed air is supplied to form the air cushion primarily through orifices or slots in the bottom portion of each cell. In this case, air is supplied successively by the injecting devices first to the cavities of the inflatable cells proper, then to form the air cushions.
It should also be noted that with two inflatable cells each injecting device feeds air simultaneously to both cells and the cavities of these cells communicate with each other.
The deceleration of the aircraft running on the landing gear by employing the air cushion effect is accomplished either through friction between the runway surface and the bottom portions of the inflatable cells contacting therewith during deceleration, or by means of inflatable high-pressure balloons circumscribing the bottom portions of the cells.
The controllability of the aircraft during take-off run, landing run and taxiing on an airfield is accomplished by varying the value of the braking forces provided by said high-pressure balloons on the left- and right-hand sides of the inflatable cells.
The retraction of the inflatable cells in flight takes place in the prior-art landing gears due to the elastic properties of the materials from which they are made. After compressed air supply is cut off, the cells are pressed or collapsed against the surface of the aircraft's fuselage.
The prior-art air-cushion landing gears suffer from a number of disadvantages of which the most serious are as follows:
the employment of inflatable cells of a longitudinally extended shape deteriorates the conditions of "maintaining" the air cushion as the cells approach the runway surface and deflect during landing at a particular angle of pitch, thereby reducing the operational efficiency of the air cushion as a landing impact-attenuation system.
The latter disadvantage is aggravated by the absence of longitudinal sectioning of the cavities of the air cushion and the inflatable cell (cf. the landing gear of the "La-4" aircraft) which not only decreases the lift of the cushion proper and lowers the vertical stiffness of the cell as its rear portions deflect when the aircraft is in the above-mentioned position, but can also substantially alter the function of the aircraft's nosing down during landing as compared to the same process in the case of an aircraft with a conventional wheeled landing gear.
In a landing gear where the air cushion is divided into two spaces (cf. U.S. Pat. No. 3,275,270), the aforementioned disadvantages are partially eliminated due to the pneumatic communication between the inflatable cells confining the air cushion.
The shape and design features of the cells under consideration, the air cushions confined therebetween and the system of supplying air to both impose certain restrictions on the possibilities of optimizing the type and completeness of the diagram of dynamic deflection of the air-cushion landing gear units.
The above reasons for decreasing the vertical and moment stiffness of the landing gear units in the two considered diagrams with the track of these landing gears being considerably narrowed, call for a certain reduction in the transverse restoring moment during landing with a ground roll. It should also be noted here that the effective width (the width along the lines of contact between the curtain and the runway surface at zero hover height and the air cushion area) are inconsistent with the large transverse dimensions of the prior-art inflatable cells, as well as with their dimensions in plan, and the resulting mid-section, surface dimensions and weight of the cells.
Finally, to provide for allowable clearance between the elements of the aircraft structure and the runway surface during a maximum landing deflection of the rear portions of the cells (with the above-described designs of these cells, methods of their sectioning and supply of compressed air), a need arises to considerably increase the pressure in the cells with respect to the pressure in the air cushions or to increase the height of the cells along the entire perimeter with respect to the required height in case the aircraft moves on the landing gear with zero angles of pitch (e.g. while taxiing on an airfield).
However, an increase in pressure in the cells is associated with an appropriate increase in the output of the injecting devices, and an increase in the height of the cells, with an increase in their dimensions and the mid-section, both increases involving a greater weight of the landing gear structure.
A serious disadvantage of the prior-art air-cushion landing gears also lies in the system of supplying compressed air to the air cushion spaces when all or almost all air from the injecting devices is pumped through the cavities of the inflatable cells and further through numerous openings in the lower portions of each cell to their air cushion spaces. Such a system, as well as the need to compensate for losses in relatively long air ducts (cf. U.S. Pat. No. 3,275,270) require a considerable increase in the drive output of the injecting devices and in their weight.
Such air supply to the air cushions is also characterised by the following disadvantage manifesting itself in service: since aircraft equipped with landing gears of the considered type are intended to be used on semi- or unprepared airfields, a large amount of soil, snow or water will inevitably work into the inflatable cells, which may eventually lead to the clogging or freezing of the openings through which air flows to the air cushion spaces.
It should be remembered that these openings are also used to supply air to the area of contact between the cells and the runway surface to reduce the wear thereof in the course of taxiing or, especially, ground roll deceleration of the aircraft. This, however, does not eliminate the necessity of protecting respective portions of the inflatable cells against wear by way of increasing the thickness of the rubber layer and even using metal plates.
Deceleration and control of an aircraft with an air-cushion landing gear by installing special high-pressure balloons on the bottom surface of the inflatable cells inevitably involves increased wear of the balloons due to small areas or friction against the runway surface, hence, high specific pressures in the area of contact therewith. To reduce the wear, those portions of the high-pressure balloons which contact the runway surface are reinforced with metal plates.
In addition, the comparatively small distance between the balloons on the left- and right-hand sides of the cells produces a negative effect on the aircraft controllability as it runs on the landing strip, and their longitudinal spacing along the lateral portions of the inflatable cells and the considerable pivotal moment that is established in this case impair the controllability of the aircraft as it performs a ground turn in position.
The diagram of retracting the inflatable cells in the prior-art landing gears has necessitated the development of a special fabric with anisotropy of elastic properties.
The inadequacy of the prior-art landing gears for parking is another disadvantage thereof. When an aircraft is parked on deflated cells on unprepared airfields, the aerodynamics of the aircraft will noticeably be impaired due to contamination and accretion of snow and ice on the bottom surface of the fuselage and the inflatable cells. Whereas adapting inflatable cells for parking will necessitate appropriate design modifications. In the latter case, there is again the danger of clogging and freezing of the openings through which air is supplied to the air cushion.
It should be noted, in conclusion, that the aforementioned disadvantages of the prior-art air-cushion landing gears rule out the possibility of applying them to the already existing aircraft or those under construction by way of appropriately modifying or perfecting the latter.